Multistage amplifier

ABSTRACT

Provided is a multistage amplifier that can achieve both utilizing in a broad bandwidth and suppressing gain reduction. The multistage amplifier includes a plurality of differential amplifiers which are connected in series; and a direct-current component limiter that cuts off a direct-current component of input signals, in which the direct-current component limiter is disposed between the plurality of differential amplifiers, and in which a transistor size of a first differential amplifier which is disposed immediately after the direct-current component limiter is equal to or greater than a transistor size of a second differential amplifier which is disposed two stages before the direct-current component limiter.

TECHNICAL FIELD

The present disclosure relates to a multistage amplifier and, forexample, a multistage amplifier that amplifies signals in wirelesscommunication.

BACKGROUND ART

A differential amplifier has an advantage of removing common mode noiseas compared to other type of amplifier, and is widely used foramplifying baseband signals of a communication device (for example, amobile phone or a communication terminal conform to a wireless localarea network (LAN)).

As the differential amplifier in the related art, a multistage amplifieris known in which differential amplifiers are connected in multiplestages, and Inverse Scaling is applied (for example, see NPL 1). In theInverse Scaling of NPL 1, a circuit is designed in such a manner that atransistor size of the differential amplifier of each stage is reducedby half in order toward the subsequent stage.

Further, a multistage amplifier is known in which differentialamplifiers are connected in multiple stages and a DC offset of thedifferential amplifier of each stage is corrected by calibration (forexample, see PTL 1).

CITATION LIST Patent Literature

-   [PTL 1] JP-A-2011-055055 Non Patent Literature-   [NPL 1] Eduard Sackinger and Wilhelm C. Fischer, “A 3-GHz 32-dB CMOS    Limiting Amplifier for SONET OC-48 Receivers”, IEEEJOURNAL OF    SOLID-STATE CIRCUITS, DECEMBER 2000, vol. 35, NO. 12. P 1884-P 1888.

SUMMARY OF INVENTION Technical Problem

In NPL 1 and PTL 1, when the multistage amplifier is utilized in a broadbandwidth, a gain of the multistage amplifier is reduced.

The present disclosure is made in view of the above circumstance, andprovides a multistage amplifier that can achieve both utilizing in abroad bandwidth and suppressing gain reduction.

Solution to Problem

A multistage amplifier according to the present disclosure includes aplurality of differential amplifiers which are connected in series; anda direct-current component limiter that cuts off a direct-currentcomponent of input signals, in which the direct-current componentlimiter is disposed between the plurality of differential amplifiers,and in which a transistor size of a first differential amplifier whichis disposed immediately after the direct-current component limiter isequal to or greater than a transistor size of a second differentialamplifier which is disposed two stages before the direct-currentcomponent limiter.

Advantageous Effects of Invention

According to the present disclosure, it is possible to achieve bothutilizing in a broad bandwidth and suppressing gain reduction.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a circuit diagram illustrating a circuit configuration exampleof a multistage amplifier in a first embodiment.

FIG. 2 is a circuit diagram illustrating a configuration example of ahigh pass filter (HPF) that is included in the multistage amplifier inthe first embodiment.

FIG. 3 is a schematic diagram illustrating examples of a transistor sizeand a variation of a direct current (DC) offset of the multistageamplifier in the first embodiment.

FIG. 4 is a schematic diagram illustrating examples of a transistor sizeand a variation of a DC offset of a multistage amplifier of the relatedart when a circuit is configured similar to the multistage amplifier inthe first embodiment.

FIG. 5 is a circuit diagram illustrating Modification 1 of the circuitconfiguration of the multistage amplifier in the first embodiment.

FIG. 6 is a circuit diagram illustrating Modification 2 of the circuitconfiguration of the multistage amplifier in the first embodiment.

FIG. 7 is a circuit diagram illustrating a circuit configuration exampleof a multistage amplifier in a second embodiment.

FIG. 8 is a circuit diagram illustrating a circuit configuration exampleof a multistage amplifier in a third embodiment.

FIG. 9 is a circuit diagram illustrating a circuit configuration exampleof a multistage amplifier in a fourth embodiment.

FIG. 10 is a circuit diagram illustrating a circuit configurationexample of a multistage amplifier in a fifth embodiment.

FIG. 11 is a circuit diagram illustrating a circuit configurationexample of a transistor level of a variable gain amplifier of typeCherry-Hooper in the fifth embodiment.

FIG. 12 is a circuit diagram illustrating a circuit configurationexample of a multistage amplifier of a sixth embodiment.

FIG. 13 is a schematic diagram illustrating examples of a transistorsize, a variation of a DC offset, and an IQ (In-phase Quadrature-Phase)amplitude error worst value of the multistage amplifier in the sixthembodiment.

FIG. 14 is a schematic diagram illustrating examples of a transistorsize, a variation of a DC offset, and an IQ amplitude error worst valueof a multistage amplifier of the related art when a circuit isconfigured similar to the multistage amplifier of the sixth embodiment.

FIG. 15 is a schematic diagram illustrating an example of misalignmentof IQ signals.

FIG. 16 is a schematic diagram illustrating an example of a relationshipbetween a bandwidth and a parasitic capacitance of the differentialamplifier.

FIG. 17 is a circuit diagram illustrating a circuit configurationexample of a transistor level of the differential amplifier.

FIG. 18 is a schematic diagram illustrating an example of a relationshipbetween a DC offset and a probability of occurrence of the DC offset.

FIG. 19 is a schematic diagram illustrating an example of a variation ofthe DC offset for a transistor size.

FIG. 20 is a schematic diagram illustrating an example of a gaincharacteristic of a differential amplifier with respect to the DC offsetwhich is inputted to the differential amplifier.

FIG. 21 is a circuit diagram illustrating a configuration of amultistage amplifier of NPL 1 to which Inverse Scaling is applied.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be describedwith reference to the drawings.

(Background for Achieving an Aspect of the Present Disclosure)

For example, a short-range wireless system of a millimeter wave bandconforming to IEEE802.11 processes baseband signals of broadband (forexample, 880 MHz bandwidth) (hereinafter, simply, referred to as“broadband signals”). Therefore, a system handling broadband signalsrequires a broadband differential amplifier, as compared to, forexample, a differential amplifier handling baseband signals of acommunication device in the related art.

FIG. 16 is a schematic diagram illustrating a relationship between abandwidth of signals that can be processed by a differential amplifierand a parasitic capacitance of a transistor that the differentialamplifier includes. Generally, as the parasitic capacitance of thetransistor is increased, the bandwidth is reduced. Therefore, in orderto realize broad bandwidth in the differential amplifier, it isnecessary to reduce the parasitic capacitance of the transistor. Sincethe parasitic capacitance of the transistor is proportional to thetransistor size, it is necessary to reduce the transistor size in orderto reduce the parasitic capacitance.

Meanwhile, when the transistor size is reduced, the mismatch ofcharacteristics (for example, a threshold voltage) of a transistor pair(for example, input terminals M1 a and M1 b in FIG. 17) to which signalsof the differential amplifier are inputted is increased. In this case, avariation of a difference of DC voltages (hereinafter, referred to as aDC offset) on the positive side and the negative side of a differentialsignal input to the differential amplifier is increased. FIG. 17 is acircuit diagram illustrating a circuit configuration example of thedifferential amplifier.

When a plurality of transistors having same characteristics are tried tobe manufactured, a variation occurs in the characteristics (for example,a DC offset) of the transistor according to, for example, a normaldistribution. FIG. 18 is a schematic diagram illustrating a relationshipbetween a DC offset and the probability of occurrence of each DC offset.

The variation of the threshold voltage of the transistor is generallyinversely proportional to the square root of the transistor size S. Thevariation of the DC offset of the differential amplifier is generallyproportional to the variation amount of the threshold voltage of thetransistor. Therefore, the variation of the DC offset of thedifferential amplifier is inversely proportional to the square root ofthe transistor size S, as illustrated in FIG. 19.

Further, as illustrated in FIG. 20, as the absolute value of the DCoffset of the differential amplifier is increased, the gain of thedifferential amplifier is reduced; and as the absolute value of the DCoffset is reduced, the gain of the differential amplifier is increased.Therefore, when the variation of the DC offset of the differentialamplifier is increased, the gain of the differential amplifier varies,and the gain is reduced.

In this manner, there is a trade-off relationship between the expansionof the bandwidth of the differential amplifier, the variation reductionof the DC offset, and the gain reduction.

Next, technologies based on NPL 1 and PTL 1 are considered.

FIG. 21 is a circuit diagram illustrating a configuration of themultistage amplifier of NPL 1 to which Inverse Scaling is applied.

In FIG. 21, a transistor size of a differential amplifier of a firststage is “8x”, a transistor size of a differential amplifier of a secondstage is “4x”, a transistor size of a differential amplifier of a thirdstage is “2x”, and a transistor size of a differential amplifier of afourth stage is “1x”. “x” indicates a predetermined value.

In the multistage amplifier, the parasitic capacitance of the transistorof the differential amplifier of a subsequent stage more greatlycontributes to an output of the multistage amplifier than the parasiticcapacitance of the transistor of the differential amplifier of apreceding stage. When Inverse Scaling is applied, the transistor size isreduced toward the subsequent stage, and thus the broadband can befurther expanded as compared to a case of equally configuring thetransistor size of the preceding differential amplifier.

Further, the DC offset generated by the differential amplifier and analternating current component are amplified by the differentialamplifier of each stage. Therefore, an influence of the DC offsetgenerated in the differential amplifier close to an input terminal ofthe multistage amplifier is greater than the influence of the DC offsetgenerated in the differential amplifier close to an output terminal ofthe multistage amplifier.

In the Inverse Scaling, the closer to the input terminal of themultistage amplifier, the larger the transistor size of the transistorincluded in the differential amplifier. Therefore, the closer to theinput terminal, the smaller the variation of the DC offset generated inthe differential amplifier, and the smaller the variation of the DCoffset input to the last differential amplifier of the multistageamplifier.

However, when the Inverse Scaling of NPL 1 is applied to a short-rangewireless system that performs communication in a radio frequencybandwidth including a millimeter wave band (for example, a frequencyband conforming to IEEE802.11ad), it is necessary to consider thefollowing circumstances.

In the recent communication system, the number of systems handlingbroadband signals has increased further. For example, as compared to acommunication device handling a baseband bandwidth of about 20 MHz inthe related art, a communication device performing millimeter wavecommunication handles a baseband bandwidth of about 880 MHz, such thatthe baseband bandwidth is 40 times or more. Therefore, since it isnecessary to further reduce the parasitic capacitance to satisfy thebandwidth and to further reduce the transistor size of the differentialamplifier of each stage, the variation reduction of DC offset becomesdifficult. Therefore, it is difficult to achieve both of the broadbandwidth and the gain reduction.

Further, when the broadband signals are amplified, a gain per one stageof the differential amplifier is reduced, and thus the differentialamplifiers of more stages than in the related art are connected, inorder to realize a reception sensitivity defined by the standard as thereceiver. In this case, when the Inverse Scaling is performed byimplementing the broad bandwidth, the transistor size of thedifferential amplifier close to the output terminal of the multistageamplifier is reduced. Accordingly, in the differential amplifier closeto the output terminal of the multistage amplifier, a large variation ofthe DC offset is generated and input to the differential amplifier ofthe last stage. Therefore, a variation occurs in the gain of themultistage amplifier, and the gain may be reduced.

In PTL 1, it is not possible to follow the variation in the DC offsetafter the calibration (for example, the variation due to temperaturechange), and the gain may also be reduced.

Hereinafter, a description will be made regarding a multistage amplifierthat can achieve both utilizing in the broad bandwidth and suppressinggain reduction.

The multistage amplifier in the following embodiment is mounted in awireless device conforming to the specification of Wireless Fidelity(WiFi) and Wireless Gigabit (WIGIG). Further, the multistage amplifierprocesses broad frequency signals (for example, bandwidth 100 MHz ormore).

First Embodiment

FIG. 1 is a circuit diagram illustrating a circuit configuration exampleof a multistage amplifier 1000 in a first embodiment. The multistageamplifier 1000 includes an input terminal 510 and an output terminal520. Further, the multistage amplifier 1000 includes a differentialamplifier 110 of the (1-1)-th stage, a differential amplifier 120 of the(1-2)-th stage, and a differential amplifier 130 of the (1-3)-th stage.Further, the multistage amplifier 1000 includes a differential amplifier210 of the (2-1)-th stage, a differential amplifier 220 of the (2-2)-thstage, and a differential amplifier 230 of the (2-3)-th stage. Further,the multistage amplifier 1000 includes a high pass filter (HPF) 410.FIG. 1 is an example of a multistage amplifier of six stages.

When the respective differential amplifiers (for example, thedifferential amplifiers 110, 120, 130, 210, 220, and 230) are notdistinguished particularly, they are simply referred to as “differentialamplifier 100”.

In the multistage amplifier 1000, a plurality of differential amplifiers100 are connected in series. The differential amplifiers 100 included inthe multistage amplifier 1000 are disposed while being divided intosegments depending on the input terminal, the output terminal of themultistage amplifier 1000, or the HPF. Further, a first segment Seg1, asecond segment Seg2, are arranged in this order from the input terminalto the output terminal of the multistage amplifier 1000. In FIG. 1, arange from the input terminal 510 of the multistage amplifier 1000 tothe HPF 410 is the first segment, and a range from the HPF 410 to theoutput terminal 520 of the multistage amplifier 1000 is the secondsegment.

One or more differential amplifiers are included in each segment. When aplurality of differential amplifiers are included in a segment, thedifferential amplifier of the first stage, the differential amplifier ofthe second stage, . . . are arranged in this order from the inputterminal to the output terminal of the multistage amplifier 1000.

The differential amplifier of “the (X-Y)-th stage” represents adifferential amplifier of the Y-th stage in the X-th segment.

Differential baseband signals which are inputted from the input terminal510 are outputted to the HPF 410 through the differential amplifier 110of the (1-1)-th stage, the differential amplifier 120 of the (1-2)-thstage, and the differential amplifier 130 of the (1-3)-th stage.Further, the differential baseband signals which are outputted from theHPF 410 is outputted from the output terminal 520 through thedifferential amplifier 210 of the (2-1)-th stage, a differentialamplifier 220 of the (2-2)-th stage, and a differential amplifier 230 ofthe (2-3)-th stage.

Each differential amplifier 100 is, for example, similarly configured,and the circuit thereof is configured, for example, as illustrated inFIG. 17. Input signals Vin+ that are inputted to the differentialamplifier 100 is a positive phase side of the differential basebandsignals, and input signals Vin− are a reverse phase side of thedifferential baseband signals.

The HPF 410 cuts off a direct-current component contained in signalsthat are inputted to the HPF 410. For example, the HPF 410 cuts off(cancels) the DC offset that is generated by each differential amplifierin the segment of the preceding stage and input to the HPF 410. The HPF410 is an example of a direct-current component limiter.

The HPF 410 may have a function of giving DC bias voltage (VDD) to thedifferential amplifier 210 of the (2-1)-th stage.

FIG. 2 is a circuit diagram illustrating a circuit configuration exampleof the HPF 410. The HPF 410 includes, for example, capacitors 411 and412, and coils 413 and 414. Since the HPF 410 is included, it ispossible to cancel the DC offset occurring in each differentialamplifier 100 in the first segment Seg1 which is the preceding stage, bya simple configuration. Therefore, it is possible to reduce theinfluence of the DC offset to the differential amplifier 230 of the(2-3)-th stage which is the differential amplifier of the last stage inthe second segment Seg2 and is closest to the output terminal of themultistage amplifier 1000.

Therefore, when performing the Inverse Scaling for each segment in themultistage amplifier 1000, it is possible to suppress the DC offset thatis inputted to the differential amplifier of the last stage in eachsegment. Therefore, it is possible to avoid a situation where thetransistor included in the differential amplifier of the last stage ineach segment does not operate in a desired operating area, and retain adesired gain.

Next, a description will be made regarding a setting example of thetransistor size S of the transistor included in the differentialamplifier 100.

In the present embodiment, the transistor size S is represented by, forexample, the following equation based on the gate width of at least thetransistor.S=L×W, or S=W

Here, L: gate length of a transistor, and W: gate width of a transistor.

When the transistor size S of the differential amplifier 100 of the(X-Y)-th stage is set to S_(X-Y), the transistor size is designed tosatisfy the following equations (1), in the multistage amplifier 1000.S ₁₋₁ ≥S ₁₋₂S ₂₋₁ ≥S ₂₋₂S ₂₋₁ ≥S ₁₋₂  Equations (1)

In other words, in each segment, the transistor size of the differentialamplifier 100 is designed by the Inverse Scaling (see FIG. 3). Forexample, the transistor size of the differential amplifier 110 of the(1-1)-th stage is assumed as “16x”. “x” indicates a predetermined value.Similarly, for example, the transistor size of the differentialamplifier 120 of the (1-2)-th stage is assumed as “8x”, and thetransistor size of the differential amplifier 130 of the (1-3)-th stageis assumed as “4x”. Further, for example, the transistor size of thedifferential amplifier 210 of the (2-1)-th stage is assumed as “16x”,the transistor size of the differential amplifier 220 of the (2-2)-thstage is assumed as “8x”, and the transistor size of the differentialamplifier 230 of the (2-3)-th stage is assumed as “4x”.

By setting S₁₋₁≥S₁₋₂, the variation of the DC offset generated in thedifferential amplifier 110 of the (1-1)-th stage is reduced more thanthe variation of the DC offset generated in the differential amplifier120 of the (1-2)-th stage having a relatively small influence. Since theDC offset of the differential amplifier 110 of the (1-1)-th stage isalso amplified even in the differential amplifier 120 to which signalsare relayed, the influence to the variation of the DC offset that isinputted to the differential amplifier 130 of the (1-3)-th stage isgreater than the differential amplifier 120 of the (1-2)-th stage.

Therefore, since the transistor size of the differential amplifier 100in each stage gradually decreases in the first segment Seg1, it ispossible to suppress an increase in the transistor size and an increasein the parasitic capacitance. Further, it is possible to efficientlyreduce the DC offset that is inputted to the differential amplifier 130of the (1-3)-th stage.

Similarly, since the transistor size of the differential amplifier 100in each stage gradually decreases in the second segment Seg2 by settingS₂₋₁≥S₂₋₂, it is possible to suppress an increase in the transistor sizeand an increase in the parasitic capacitance. Further, it is possible toefficiently reduce the DC offset that is inputted to the differentialamplifier 230 of the (2-3)-th stage.

Further, the transistor sizes of the differential amplifiers 210 and 220of the subsequent stages can be designed to be greater than the HPF 410which has been designed to be significantly small in a case of applyingthe Inverse Scaling in the related art, by setting S₂₋₁≥S₁₋₂. Thus, itis possible to reduce the variation of the DC offset that is inputted tothe differential amplifier 230 of the (2-3)-th stage.

In addition, the condition of S₁₋₂≥S₁₋₃ may be satisfied or notsatisfied. In other words, the transistor size of any one (here, thedifferential amplifier 110) of differential amplifiers from the firststage to two stages before the last stage in the segment may be equal toor greater than the transistor size of the differential amplifier (here,the differential amplifier 120) disposed immediately after thedifferential amplifier. Further, the transistor size of the differentialamplifier (here, differential amplifier 120) which is the second stagefrom the last stage in the segment may not be equal to or greater thanthe transistor size of the differential amplifier (here, differentialamplifier 130) disposed immediately after the differential amplifier.Even in this case, the DC offset that is outputted from the differentialamplifier 130 of the last stage can be cut off by the HPF 410 disposedimmediately after the differential amplifier 130, and the influence ofthe DC offset to the subsequent segment can be suppressed.

In addition, the differential amplifier 210 of the (2-1)-th stage is anexample of the first differential amplifier that is disposed immediatelyafter the direct-current component limiter. The differential amplifier120 of the (1-2)-th stage is an example of the second differentialamplifier that is disposed two stages before the direct-currentcomponent limiter.

In this manner, since it is possible to reduce the variation of the DCoffsets that are inputted to the differential amplifiers 130 and 230 ofthe last stages in the respective segments, it is possible to suppress adecrease in the gain of the multistage amplifier 1000.

Next, a description will be made regarding the transistor size and thevariation of the DC offsets of the multistage amplifiers of the presentembodiment and in the related art.

FIG. 3 is a schematic diagram illustrating an example of the transistorsize S and the variation of the DC offset of the multistage amplifier1000 of the present embodiment. FIG. 4 is a schematic diagramillustrating an example of the transistor size S and the variation ofthe DC offset of a multistage amplifier obtained by inserting the HPFinto the multistage amplifier in the related art, similar to themultistage amplifier 1000. FIGS. 3 and 4 are diagrams illustratingexamples of simulation results.

Here, the transistor sizes are set in such a manner that the bandwidthsin consideration of the parasitic capacitances of the transistors ineach differential amplifier are the same in the present embodiment andthe related art. Further, the parasitic capacitance of the drainterminal of the transistor per one transistor in each differentialamplifier is assumed as 0.7 fF, and the parasitic capacitance of thegate terminal is assumed as 1.4 fF.

In the multistage amplifier 1000 of FIG. 3, in each segment, thetransistor size of the differential amplifier 100 is designed by theInverse Scaling. In the multistage amplifier of FIG. 4, the transistorsize of the differential amplifier, from the input terminal to theoutput terminal of the multistage amplifier, is designed by the InverseScaling.

For example, in FIG. 4, the transistor size of the differentialamplifier of the (1-1)-th stage is assumed as “32x”, the transistor sizeof the differential amplifier of the (1-2)-th stage is assumed as “16x”,and the transistor size of the differential amplifier of the (1-3)-thstage is assumed as “8x”. Further, the transistor size of thedifferential amplifier of the (2-1)-th stage is assumed as “4x”, thetransistor size of the differential amplifier of the (2-2)-th stage isassumed as “2x”, and the transistor size of the differential amplifierof the (2-3)-th stage is assumed as “1x”.

In the simulation, the input of the differential amplifier of the laststage in each segment (for example, the differential amplifier of the(1-3)-th stage, and the differential amplifier of the (2-3)-th stage) isperformed using a test device which is not illustrated. The test devicemeasures, for example, the DC offset characteristics of a plurality ofsamples (integrated circuits (IC) of a plurality of multistageamplifiers 100). Then, the test device derives a difference between amaximum value (for example, +3σ value) and a minimum value (for example,−3σ value) of the DC offset of each measured result, as the variation ofthe DC offset.

The variations of the DC offsets are compared. The variation of the DCoffset that is inputted to the differential amplifier of the (1-3)-thstage is 98 mV in the present embodiment, and 70 mV in the related artmethod. Therefore, it is possible to understand that the variation ofthe DC offset in the present embodiment is slightly larger than in therelated art.

The variation of the DC offset that is inputted to the differentialamplifier of the (2-3)-th stage is 98 mV in the present embodiment, and196 mV in the related art method. Therefore, it is possible tounderstand that the variation of the DC offset in the present embodimentis significantly smaller than in the related art, and is reduced byabout half.

According to the multistage amplifier 1000, it is possible to suppress again variation due to a variation of the DC offset of each differentialamplifier 100. Thus, for example, it is possible to reduce a margin ofeach differential amplifier 100 at a time of design, and powerconsumption.

Further, for example, an increase in the number of stages of thedifferential amplifier 100 is expected in a short-range wireless systemusing a radio frequency band including a millimeter wave band, but thevariation of the DC offset in each segment can be reset according to themultistage amplifier 1000. Therefore, even when the number of stages ofthe differential amplifier 100 is increased, the variation of the DCoffset is not increased, and it is possible to achieve both broadbandwidth and gain reduction suppression. The short-range wirelesssystem described above is a system using, for example, IEEE802.11ad.

Further, in order to suppress the DC offset, it is possible to assumethat the direct-current component is cut off by the HPF in eachdifferential amplifier 100, but in this case, the number of circuitelements is increased, and thus it is difficult to miniaturize themultistage amplifier. According to the multistage amplifier 1000,miniaturization of the circuit scale can be realized.

Further, since the HPF is inserted into the multistage amplifier 4000 inthe right place, the DC offset can be cut off at a proper time, and theDC offset can be prevented from being excessively increased. Therefore,the inputs to the differential amplifier of the last stage can beprevented from being saturated.

(Modification 1)

As illustrated in FIG. 5, the multistage amplifier 1000 may be amultistage amplifier 1000A in which an HPF 420 is inserted between theinput terminal 510 and the differential amplifier 110 of the (1-1)-thstage. Thus, the DC offset from the preceding stage of the multistageamplifier 1000 can be suppressed. For example, when the multistageamplifier 1000 is mounted in the receiver, the preceding stage of themultistage amplifier 1000 is, for example, a low noise amplifier (LNA)or a mixer.

(Modification 2)

As illustrated in FIG. 6, the multistage amplifier 1000 may be amultistage amplifier 1000B in which an HPF 430 is inserted between thedifferential amplifier 230 of the (2-3)-th stage and the output terminal520. Thus, the DC offset to be outputted to the subsequent stage of themultistage amplifier 1000 can be suppressed. For example, when themultistage amplifier 1000 is mounted in the receiver, the subsequentstage of the multistage amplifier 1000 is, for example, an analog todigital converter (ADC) or a digital circuit.

(Modification 3)

Further, suppressing the DC offset by the HPF 410 has been exemplified,but the DC offset may be suppressed by other methods. For example, thedifferential output of one of the differential amplifiers 100 isbranched for detecting the DC offset, and only a DC component isextracted by a low pass filter (LPF). Further, the parameters (forexample, a resistance value) of the differential amplifier 100 or thepreceding stage differential amplifier 100 of the differential amplifier100 may be adjusted and the DC offset may be cancelled.

In addition, Modifications 1 to 3 may be combined as appropriate.

Second Embodiment

FIG. 7 is a circuit diagram illustrating a circuit configuration exampleof a multistage amplifier 2000 in a second embodiment. The configurationand operation of the multistage amplifier 2000 are the same as theconfiguration and operation of the multistage amplifier 1000 describedin the first embodiment. In FIG. 7, the same components as those of themultistage amplifier 1000 in FIG. 1 are denoted by the same referencenumerals and signs, and thus the description thereof will be omitted orsimplified. In addition, the multistage amplifier 2000 may have the sameconfiguration as that of the multistage amplifier 1000A or 1000B, or thecombination described in the first embodiment.

The multistage amplifier 2000 includes, for example, an HPF 440 and athird segment Seg3 in addition to the configuration of the multistageamplifier 1000. The third segment Seg3 includes a differential amplifier310 of the (3-1)-th stage, a differential amplifier 320 of the (3-2)-thstage, and a differential amplifier 330 of the (3-3)-th stage.

Differential baseband signals which are inputted from the input terminal510 are outputted to the HPF 440 through each differential amplifier 100of the first segment Seg1, the HPF 410, and each differential amplifier100 of the second segment Seg2. In addition, differential basebandsignals which have been output from the HPF 440 are outputted from theoutput terminal 520, through each differential amplifier 100 of thethird segment Seg3. In the third segment Seg3, signals are transmittedin the order of the differential amplifier 310 of the (3-1)-th stage,the differential amplifier 320 of the (3-2)-th stage, and thedifferential amplifier 330 of the (3-3)-th stage.

Next, a description will be made regarding a setting example of thetransistor size S of the transistor included in the differentialamplifier 100.

When the transistor size S of the differential amplifier 100 of the(X-Y)-th stage is set to S_(X-Y), the transistor size is designed tosatisfy the following equation (2), in the multistage amplifier 2000.S ₁₋₁ ≥S ₁₋₂S ₂₋₁ ≥S ₂₋₂S ₃₋₁ ≥S ₃₋₂S ₂₋₁ ≥S ₁₋₂S ₃₋₁ ≥S ₂₋₂  Equations (2)

In other words, in each segment, the transistor size of the differentialamplifier 100 is designed by the Inverse Scaling. In Equation 2,S₃₋₁≥S₃₋₂ and S₃₋₁≥S₂₋₂ are added to Equation 1.

By setting S₃₋₁≥S₃₋₂, similar to S₁₋₁≥S₁₋₂, the variation of the DCoffset generated in the differential amplifier 310 of the (3-1)-th stageis reduced further than the variation of the DC offset of thedifferential amplifier 320 of the (3-2)-th stage having a relativelysmall influence. Since the DC offset of the differential amplifier 310of the (3-1)-th stage is also amplified even in the differentialamplifier 320 to which signals are relayed, the influence to thevariation of the DC offset that are inputted to the differentialamplifier 330 of the (3-3)-th stage is greater than that of thedifferential amplifier 320 of the (3-2)-th stage.

Therefore, since the transistor size of the differential amplifier 100in each stage gradually decreases in the third segment Seg3, it ispossible to suppress an increase in the transistor size and an increasein the parasitic capacitance. Further, it is possible to efficientlyreduce the DC offset that is inputted to the differential amplifier 330of the (3-3)-th stage.

Further, the transistor size of the differential amplifiers 310 and 320of the subsequent stages can be designed to be greater than the HPF 440which has been designed to be significantly small in a case of applyingthe Inverse Scaling in the related art, by setting S₃₋₁≥S₂₋₂. Thus, itis possible to reduce the variation of the DC offset that is inputted tothe differential amplifier 330 of the (3-3)-th stage.

In this manner, since it is possible to reduce the variation of the DCoffsets that are inputted to the differential amplifiers 130, 230, and330 of the last stages in the respective segments, it is possible tosuppress a decrease in the gain of the multistage amplifier 2000.

Further, in the present embodiment, an example in which there are twoHPFs between respective segments has been exemplified, but the presentdisclosure is not limited to this. For example, an HPF and differentialamplifiers in a fourth segment may be added, and many HPFs anddifferential amplifiers may be added.

Third Embodiment

FIG. 8 is a circuit diagram illustrating a circuit configuration exampleof a multistage amplifier 3000 in a third embodiment. The configurationand operation of the multistage amplifier 3000 are the same as theconfiguration and operation of the multistage amplifier 1000 describedin the first embodiment. In FIG. 8, the same components as those ofmultistage amplifier 1000 in FIG. 1 are denoted by the same referencenumerals and signs, and thus the description thereof will be omitted orsimplified. In addition, the multistage amplifier 3000 may have the sameconfiguration as that of the multistage amplifier 1000A or 1000B, or thecombination described in the first embodiment.

The multistage amplifier 3000 is different from the multistage amplifier1000 in the number of differential amplifiers 100 disposed in eachsegment. The multistage amplifier 3000 includes a differential amplifier140 of the (1-4)-th stage and a differential amplifier 240 of the(2-4)-th stage, in addition to the configuration of the multistageamplifier 1000.

Differential baseband signals which are inputted from the input terminal510 are outputted to the HPF 410 through the differential amplifier 110of the (1-1)-th stage, the differential amplifier 120 of the (1-2)-thstage, the differential amplifier 130 of the (1-3)-th stage, and thedifferential amplifier 140 of the (1-4)-th stage. In addition,differential baseband signals which have been output from the HPF 410are outputted from the output terminal 520, through the differentialamplifier 210 of the (2-1)-th stage, the differential amplifier 220 ofthe (2-2)-th stage, the differential amplifier 230 of the (2-3)-thstage, and the differential amplifier 240 of the (2-4)-th stage.

Next, a description will be made regarding a setting example of thetransistor size S of the transistor included in the differentialamplifier 100.

When the transistor size S of the differential amplifier 100 of the(X-Y)-th stage is set to S_(X-Y), the transistor size is designed tosatisfy the following equation (3), in the multistage amplifier 3000.S ₁₋₁ ≥S ₁₋₂ ≥S ₁₋₃S ₂₋₁ ≥S ₂₋₂ ≥S ₂₋₃S ₂₋₁ ≥S ₁₋₃  (Equation 3)

In other words, in each segment, the transistor size of the differentialamplifier 100 is designed by the Inverse Scaling.

By setting S₁₋₁≥S₁₋₂≥S₁₋₃, the variation of the DC offset generated inthe differential amplifier 110 of the (1-1)-th stage is reduced furtherthan the variation of the DC offset of the differential amplifier 120 ofthe (1-2)-th stage having an influence smaller than that of thedifferential amplifier 110. Further, the variation of the DC offsetgenerated in the differential amplifier 120 of the (1-2)-th stage isreduced further than the variation of the DC offset of the differentialamplifier 130 of the (1-3)-th stage having an influence smaller thanthat of the differential amplifier 120.

Since the DC offset of the differential amplifier 110 of the (1-1)-thstage is also amplified even in the differential amplifier 120 to whichsignals are relayed, the influence to the variation of the DC offsetthat are inputted to the differential amplifier 140 of the (1-4)-thstage is greater than that of the differential amplifier 120 of the(1-2)-th stage. Further, since the DC offset of the differentialamplifier 110 of the (1-2)-th stage is also amplified even in thedifferential amplifier 130 to which signals are relayed, the influenceto the variation of the DC offset that is inputted to the differentialamplifier 140 of the (1-4)-th stage is greater than that of thedifferential amplifier 130 of the (1-3)-th stage.

Therefore, since the transistor size of the differential amplifier 100in each stage gradually decreases in the first segment Seg1, it ispossible to suppress an increase in the transistor size and an increasein the parasitic capacitance. Further, it is possible to efficientlyreduce the DC offset that is inputted to the differential amplifier 140of the (1-4)-th stage.

Similarly, since the transistor size of the differential amplifier 100in each stage gradually decreases in the second segment Seg2 by settingS₂₋₁≥S₂₋₂≥S₂₋₃, it is possible to suppress an increase in the transistorsize and an increase in the parasitic capacitance. Further, it ispossible to efficiently reduce the DC offset that is inputted to thedifferential amplifier 240 of the (2-4)-th stage.

Further, the transistor sizes of the differential amplifiers 210, 220,and 230 of the subsequent stages can be designed to be greater than theHPF 410 which has been designed to be significantly small in a case ofapplying the Inverse Scaling in the related art, by setting S₂₋₁≥S₁₋₃.Thus, it is possible to reduce the variation of the DC offset that isinputted to the differential amplifier 240 of the (2-4)-th stage.

Further, in the present embodiment, an example has been exemplified inwhich the number of HPFs is one and the number of stages of thedifferential amplifier is eight in total. In addition thereto, forexample, an HPF is present between one or more stages, and differentialamplifiers of three stages or more may be present in at least twopositions (two segments) among between the input terminal 510 and theHPF, between a plurality of HPFs, and between the HPF and the outputterminal 520. Even in this case, the effect of the present embodiment isachieved, and thus it is possible to achieve both utilizing in the broadbandwidth and suppressing gain reduction of the multistage amplifier4000.

Fourth Embodiment

FIG. 9 is a circuit diagram illustrating a circuit configuration exampleof a multistage amplifier 4000 in a fourth embodiment. The configurationand operation of the multistage amplifier 4000 are the same as theconfiguration and operation of the multistage amplifier 1000 describedin the first embodiment. In FIG. 9, the same components as those of themultistage amplifier 1000 in FIG. 1 are denoted by the same referencenumerals and signs, and thus the description thereof will be omitted orsimplified. In addition, the multistage amplifier 4000 may have the sameconfiguration as that of the multistage amplifier 1000A or 1000B, or thecombination described in the first embodiment.

The multistage amplifier 4000 is different from the multistage amplifier1000 illustrated in FIG. 1 in that the differential amplifier 100 ineach stage is a variable gain amplifier (VGA) 150.

Since each differential amplifier 100 is the variable gain amplifier150, it is possible to change the gain of the multistage amplifier 4000.Thus, a desired gain can be adjusted, and it is possible to achieve bothutilizing in a broad bandwidth and suppressing gain reduction.

The gain reduction due to the variation of the DC offset in themultistage amplifier 4000 is maximized when the gain of the variablegain amplifier 150 is set to a maximum value. When a setting of the gainof the multistage amplifier 4000 is fixed to, for example, a maximumvalue, the multistage amplifier 4000 operates similarly to themultistage amplifier 1000 in the first embodiment. For example, sincethe gain of the multistage amplifier 4000 is fixed to the maximum valueand the differential amplifier 100 included in the multistage amplifier4000 is set to the transistor size based on (Equation 1), the sameeffect as FIG. 3 described in the first embodiment is obtained.

In addition, in FIG. 9, although the example is illustrated in which thedifferential amplifiers 100 of all stages in the multistage amplifier4000 are variable gain amplifiers 150, it is not limited thereto. Forexample, even when a portion of the differential amplifiers 100 are thevariable gain amplifiers 150 and the remaining differential amplifiers100 are gain-fixed differential amplifiers 100, the same effect can beobtained.

Fifth Embodiment

FIG. 10 is a circuit diagram illustrating a circuit configurationexample of a multistage amplifier 5000 in a fifth embodiment. Themultistage amplifier 5000 is different from the multistage amplifier4000 in the fourth embodiment in that the differential amplifiers 100 ofthe stages of a portion are a variable gain amplifier of typeCherry-Hooper 150A.

FIG. 11 is a circuit diagram illustrating a circuit configurationexample of a transistor level of the variable gain amplifier of typeCherry-Hooper 150A. The variable gain amplifier of type Cherry-Hooper150A includes differential amplifiers 151 of a first stage includinginput terminals M1 a and M1 b, differential amplifiers 152 of a secondstage including input terminals M2 a and M2 b, and a feedback resistorR_(f). In other words, the variable gain amplifier of type Cherry-Hooper150A includes the differential amplifiers 151 and 152 of two stages, andcontrols the gain of the feedback resistor R_(f).

The operation and effect of the multistage amplifier 5000 is the same asthat of the multistage amplifier 4000, and thus a description thereofwill be omitted.

Sixth Embodiment

FIG. 12 is a circuit diagram illustrating a circuit configurationexample of a multistage amplifier 6000 in a sixth embodiment. Themultistage amplifier 6000 includes an I-side multistage amplifier 6000Athat processes I signals out of IQ signals, and Q-side multistageamplifier 6000B that processes Q signals.

The configuration and operation of the I-side multistage amplifier 6000Aand the Q-side multistage amplifier 6000B are the same as theconfiguration and operation of any of the multistage amplifiers in anyof the first to fifth embodiments, thus the detailed description thereofwill be omitted or simplified. It is exemplified that the presentembodiment is the same as the multistage amplifier 1000 of the firstembodiment in the configuration and operation.

In the I-side multistage amplifier 6000A and the Q-side multistageamplifier 6000B of FIG. 12, some reference numerals are changed from themultistage amplifier 1000 of FIG. 1. For example, “a” and “b” arerespectively added to the I-side and the Q-side.

The I-side multistage amplifier 6000A includes an input terminal 510 aand an output terminal 520 a. Further, the I-side multistage amplifier6000A includes a differential amplifier 110 a of the (1-1)-th stage, adifferential amplifier 120 a of the (1-2)-th stage, and a differentialamplifier 130 a of the (1-3)-th stage. Further, the I-side multistageamplifier 6000A includes a differential amplifier 210 a of the (2-1)-thstage, a differential amplifier 220 a of the (2-2)-th stage, and adifferential amplifier 230 a of the (2-3)-th stage. Further, the I-sidemultistage amplifier 6000A includes an HPF 410 a. The I-side multistageamplifier 6000A amplifies the I-side signals (I signals) of differentialbaseband signals.

The Q-side multistage amplifier 6000B includes an input terminal Sloband an output terminal 520 b. Further, the Q-side multistage amplifier6000B includes a differential amplifier 110 b of the (1-1)-th stage, adifferential amplifier 120 b of the (1-2)-th stage, and a differentialamplifier 130 b of the (1-3)-th stage. Further, the Q-side multistageamplifier 6000B includes a differential amplifier 210 b of the (2-1)-thstage, a differential amplifier 220 b of the (2-2)-th stage, and adifferential amplifier 230 b of the (2-3)-th stage. Further, the Q-sidemultistage amplifier 6000B includes an HPF 410 b. The Q-side multistageamplifier 6000B amplifies the Q-side signals (Q signals) of differentialbaseband signals.

Next, a description will be made regarding the transistor size S, thevariation of the DC offset, and an IQ amplitude error worst value of themultistage amplifier 6000 in the present embodiment and the related art.

FIG. 13 is a schematic diagram illustrating the transistor size S, thevariation of the DC offset, and the IQ amplitude error worst value ofthe multistage amplifier 6000 in the present embodiment. FIG. 14 is aschematic diagram illustrating the transistor size S, the variation ofthe DC offset, and the IQ amplitude error worst value of the multistageamplifier in the related art. FIGS. 13 and 14 are diagrams illustratingexamples of simulation results.

Here, the transistor sizes are set in such a manner that the bandwidthsin consideration of the parasitic capacitances of the transistors ineach differential amplifier 100 are the same in the present embodimentand the related art. Further, the parasitic capacitance of the drainterminal of the transistor per one transistor in each differentialamplifier 100 is assumed as 0.7 fF, and the parasitic capacitance of thegate terminal is assumed as 1.4 fF.

In the multistage amplifier 6000 of FIG. 13, even in each segment ofeither the I-side multistage amplifier 6000A or the Q-side multistageamplifier 6000B, the transistor size of the differential amplifier 100is designed by the Inverse Scaling.

In the multistage amplifier 6000 of FIG. 14, even in either the I-sidemultistage amplifier 6000A or the Q-side multistage amplifier 6000B, thetransistor size of the differential amplifier 100, from the inputterminal to the output terminal of the multistage amplifier, is designedby the Inverse Scaling.

In the simulation, the input of the differential amplifier of the laststage in each segment (for example, the differential amplifiers 130 aand 130 b of the (1-3)-th stage, and the differential amplifiers 230 aand 230 b of the (2-3)-th stage) is performed using a test device whichis not illustrated.

The test device measures, for example, the DC offset characteristics ofa plurality of samples (the IC of a plurality of the I-side multistageamplifier 6000A and the IC of a plurality of the Q-side multistageamplifier 6000B). Then, the test device derives a difference between amaximum value (for example, +3σ value) and a minimum value (for example,−3σ value) of the DC offset of each measured result, as the variation ofthe DC offset.

Further, a plurality of sample signals are inputted to the I-sidemultistage amplifier 6000A, and the I signals of sample signals aresequentially measured. The measured I signals are signals which areinputted to the differential amplifier of the last stage in eachsegment, or output from the differential amplifier.

Similarly, a plurality of sample signals are inputted to the Q-sidemultistage amplifier 6000B, and the Q signals of sample signals aresequentially measured. The measured Q signals are signals which areinputted to the differential amplifier of the last stage in eachsegment, or output from the differential amplifier.

The difference between the amplitudes of the measured I signals and Qsignals are derived as an IQ amplitude error (IQ imbalance). Further,the maximum value of the IQ amplitude error among a plurality of IQamplitude errors as the simulation result is derived as the IQ amplitudeerror worst value. In addition, the IQ amplitude error is a differencedue to dbm of, for example, the I signals and the Q signals.

The transistor size and the variation of DC offset are the same as inthe first embodiment.

The IQ amplitude error worst values are compared. The IQ amplitude errorworst values of the differential amplifier of the (1-3)-th stage are 0.8dB in the present embodiment and 0.6 dB in the related art method. TheIQ amplitude error worst values of the differential amplifier of the(2-3)-th stage are 0.8 dB in the present embodiment and 3.0 dB in therelated art method.

Since the IQ amplitude error worst value of the entire multistageamplifier is a total value of the IQ amplitude error worst values of thedifferential amplifier of the last stage in each segment, it is 1.6 dBin the present embodiment and 3.6 dB in the related art method. In otherwords, the IQ amplitude error worst value of the present embodiment is 2dB smaller than that in the related art.

Thus, according to the multistage amplifier 6000, it is possible toreduce the IQ amplitude error, in addition to the effects described inthe first to fifth embodiments. Further, the IQ amplitude error can bereduced, as illustrated in FIG. 15, and it is possible to prevent thesignal point from being shifted from a desired position due to the errorcomponent, and suppress the deterioration of the bit error rate.Therefore, it is possible to achieve both an utilization of themultistage amplifier 6000 in a broad bandwidth and reduction in the IQamplitude error.

In addition, when the differential amplifier 100 is the variable gainamplifier 150, the deterioration of the IQ amplitude error due to thevariation of the DC offset is maximized when the gain of the variablegain amplifier 150 is set to a maximum value. When the setting of thegain of the multistage amplifier 6000 is fixed to, for example, themaximum value, similar to FIG. 13, the variation of the DC offset is theIQ amplitude error worst value.

(Overview of an Aspect of the Present Disclosure)

A first multistage amplifier of the present disclosure includes aplurality of differential amplifiers which are connected in series; anda direct-current component limiter that cuts off a direct-currentcomponent of input signals, in which the direct-current componentlimiter is disposed between the plurality of differential amplifiers,and in which a transistor size of a first differential amplifier whichis disposed immediately after the direct-current component limiter isequal to or greater than a transistor size of a second differentialamplifier which is disposed two stages before the direct-currentcomponent limiter.

Further, a second multistage amplifier of the present disclosure is thefirst multistage amplifier, in which in a segment indicating a rangebetween the direct-current component limiter, and one of an inputterminal of the multistage amplifier, another direct-current componentlimiter, and an output terminal of the multistage amplifier, atransistor size of a predetermined differential amplifier is equal to orgreater than the transistor size of a differential amplifier which isdisposed immediately after the predetermined differential amplifier.

Further, a third multistage amplifier of the present disclosure is thesecond multistage amplifier, in which the predetermined differentialamplifier is a differential amplifier which is disposed in any stagefrom a first stage to a stage excluding last two stages in the segment.

Further, a fourth multistage amplifier of the present disclosure is anyof the first to third multistage amplifiers, in which when a rangebetween the direct-current component limiter, and one of an inputterminal of the multistage amplifier, another direct-current componentlimiter, and an output terminal of the multistage amplifier is assumedas a segment, at least three differential amplifiers are disposed ineach of at least two segments.

Further, a fifth multistage amplifier of the present disclosure is anyof the first to fourth multistage amplifiers, in which thedirect-current component limiter is included in a plurality ofdirect-current component limiters, and in which a first direct-currentcomponent limiter is disposed immediately after an input terminal of themultistage amplifier.

Further, a sixth multistage amplifier of the present disclosure is anyof the first to fifth multistage amplifiers, in which the direct-currentcomponent limiter is included in a plurality of direct-current componentlimiters, and in which a second direct-current component limiter isdisposed immediately before an output terminal of the multistageamplifier.

Further, the seventh multistage amplifier of the present disclosure isany of the first to sixth multistage amplifiers, in which thedirect-current component limiter includes a high pass filter (HPF).

Further, the eighth multistage amplifier of the present disclosure isany of the first to seventh multistage amplifiers, in which thedifferential amplifier includes a variable gain amplifier.

Further, the ninth multistage amplifier of the present disclosure is theeighth multistage amplifier, in which the differential amplifierincludes a variable gain amplifier of type Cherry-Hooper, and in whichthe variable gain amplifier of type Cherry-Hooper includes twodifferential amplifiers.

Further, a tenth multistage amplifier of the present disclosure is anyof the first to ninth multistage amplifiers, in which there are aplurality of the multistage amplifiers, in which a first multistageamplifier amplifies I signals, and in which a second multistageamplifier amplifies Q signals.

Hitherto, although various embodiments have been described withreference to the accompanying drawings, it is needless to say that thepresent disclosure is not limited to such examples. It is obvious that aperson skilled in the art may conceive various changes and modificationswithin the scope set forth in the appended claims, and the changes andmodifications are of course understood to belong to the technical scopeof the present disclosure.

The present disclosure is based on Japanese Patent Application No.2013-022562 filed Feb. 7, 2013, and the contents of which areincorporated herein by reference.

INDUSTRIAL APPLICABILITY

The present disclosure is useful for the multistage amplifier that canachieve both utilizing in a broad bandwidth and suppressing gainreduction. For example, the present disclosure is useful as a basebandsignal differential amplifier in a wireless communication device.

REFERENCE SIGNS LIST

-   -   100, 110 a, 110 b, 120, 120 a, 120 b, 130, 130 a, 130 b, 140,        210, 210 a, 210 b, 220, 220 a, 220 b, 230, 230 a, 230 b, 240,        310, 320, 330: DIFFERENTIAL AMPLIFIER    -   150: VARIABLE GAIN AMPLIFIER    -   150A: VARIABLE GAIN AMPLIFIER OF TYPE CHERRY-HOOPER    -   410, 410 a, 410 b, 420, 430, 440: HPF    -   510, 510 a, 510 b: INPUT TERMINAL    -   520, 520 a, 520 b: OUTPUT TERMINAL    -   1000, 1000A, 1000B, 2000, 3000, 4000, 5000, 6000: MULTISTAGE        AMPLIFIER    -   6000A: I-SIDE MULTISTAGE AMPLIFIER    -   6000B: Q-SIDE MULTISTAGE AMPLIFIER    -   Seg1: FIRST SEGMENT    -   Seg2: SECOND SEGMENT    -   Seg3: THIRD SEGMENT

The invention claimed is:
 1. A multistage amplifier comprising: aplurality of differential amplifiers which are connected in series andare divided to a plurality of segments; and a first direct-currentcomponent limiter that cuts off a direct-current component of inputsignals and is disposed between the plurality of segments, wherein atransistor size of a first differential amplifier which is disposedimmediately after the first direct-current component limiter is greaterthan a transistor size of a second differential amplifier which isdisposed two stages before the first direct-current component limiter,and wherein a transistor size of a predetermined differential amplifierin a plurality of differential amplifiers included in each of thesegments is greater than a transistor size of a differential amplifierdisposed in a subsequent stage of the predetermined differentialamplifier.
 2. The multistage amplifier according to claim 1, wherein thepredetermined differential amplifier is a differential amplifier whichis disposed in any stage from a first stage to a stage excluding lasttwo stages in the segment.
 3. The multistage amplifier according toclaim 1, wherein the plurality of differential amplifiers are divided toat least two segments, and wherein each of the at least two segmentsincludes at least three differential amplifiers.
 4. The multistageamplifier according to claim 1, further comprising, a seconddirect-current component limiter is disposed immediately after an inputterminal of the multistage amplifier.
 5. The multistage amplifieraccording to claim 1, further comprising, a third direct-currentcomponent limiter is disposed immediately before an output terminal ofthe multistage amplifier.
 6. The multistage amplifier according to claim1, wherein the first direct-current component limiter includes a highpass filter (HPF).
 7. The multistage amplifier according to claim 1,wherein the differential amplifier includes a variable gain amplifier.8. The multistage amplifier according to claim 7, wherein thedifferential amplifier includes a variable gain amplifier of typeCherry-Hooper, and wherein the variable gain amplifier of typeCherry-Hooper includes two differential amplifiers.
 9. The multistageamplifier according to claim 1, wherein there are a plurality of themultistage amplifiers, wherein a first multistage amplifier amplifies Isignals, and wherein a second multistage amplifier amplifies Q signals.10. The multistage amplifier according to claim 1, wherein nodirect-current component limiter is disposed between the seconddifferential amplifier and a third differential amplifier, the thirddifferential amplifier being disposed immediately before the firstdirect-current component limiter.
 11. The multistage amplifier accordingto claim 10, wherein no direct-current component limiter is disposedbetween the plurality of differential amplifiers in each of theplurality of segments.